Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $114.72   4.186%   $119.5222   $119.52   $119.50   $119.50  
  Purchase #2 $202.53   8.669%   $220.0873   $220.09   $220.10   $220.10  
  Purchase #3 $162.27   10.574%   $179.4284   $179.43   $179.45   $179.40  
  Purchase #4 $182.65   13.496%   $207.3004   $207.30   $207.30   $207.30  
  Purchase #5 $137.75   9.712%   $151.1283   $151.13   $151.15   $151.10  
  Purchase #6 $73.31   9.792%   $80.4885   $80.49   $80.50   $80.50  
  Purchase #7 $73.41   11.142%   $81.5893   $81.59   $81.60   $81.60  
  7 purchase totals = $946.64       $1,039.5444   $1,039.55   $1,039.60   $1,039.50